Conventionally, as one method of mechanically and electrically interconnecting first and second circuit boards 8 and 9 whose surfaces are at least partially opposed to each other as shown in FIG. 7, there is known a method using a connector structure by which a first connector block 81 one-piece formed with the first circuit board 8 is connected to a second connector block 91 one-piece formed with the second circuit board 9 (see, e.g., JP Patent No. 4059522).
The first connector block 81 includes conductor protrusions 81a making electrical conduction with circuit patterns 8a of the first circuit board 8 and protruding from one surface of the first circuit board 8.
The second connector block 91 includes slit portions 9b formed in the second circuit board 9 to have a substantially cross-like shape, conductor portions 9c (see FIG. 8) formed on one surface of the second circuit board 9 along the peripheral edges of the slit portions 9b to make electrical conduction with circuit patterns 9a of the second circuit board 9, and a reinforcing plate 9e made of a substantially flat metal plate and bonded to the other surface of the second circuit board 9. The reinforcing plate 9e has insertion holes 9d formed in alignment with the slit portions 9b. 
If the conductor protrusions 81a of the first connector block 81 are inserted into the slit portions 9b at one side of the second connector block 91, the conductor protrusions 81a and the slit portions 9b are fitted and connected to each other. The conductor protrusions 81a and the conductor portions 9c make electrical conduction with each other. Thus the first circuit board 8 and the second circuit board 9 are electrically and mechanically connected to each other.
In the connector structure using the first and second connector blocks 81 and 91 one-piece formed with the first and second circuit boards 8 and 9, it is however impossible to replace only the first connector blocks 81 and/or the second connector block 91 when a trouble is generated in the first connector block 81 and/or the second connector block 91. This poses a problem in that the first circuit board 8 or the second circuit board 9 needs to be replaced as a whole.
Due to the formation of the slit portions 9b, the strength of the second circuit board 9 is reduced in the vicinity of the slit portions 9b. This imposes a restriction in that electronic parts such as an IC and the like cannot be mounted to the second circuit board 9 near the second connector block 91 having the slit portions 9b. This leads to a problem in that the degree of freedom of circuit design gets lowered.